Process and an equipment for producing crystalline citric acid from solutions of alkaline citrates

Abstract

A process for producing citric acid in crystalline form from solutions of alkaline citrates, comprising sequentially the stages of: A. partially converting by electrodialysis the alkaline citrate to citric acid; B. concentrating by hot fractional crystallization the solution of citric acid and alkaline citrate as obtained in (a); C. separating by centrifugation the crystalline citric acid from the concentrated solution coming from (b); D. re-cycling the mother liquors of crystallization residual from the separating operation (c) part to the electrodialysis stage (a) and part to the stage of crystallization (b).

Having thus described the present invention, what is claimed is: 
     
       1. A process for producing citric acid in crystalline form from solutions of alkaline citrates, characterized in comprising sequentially the stages of: a. partially converting by electrodialysis the alkaline citrate to citric acid;   b. concentrating by hot fractional crystallization the solution of citric acid and alkaline citrate as obtained in (a), heat for the crystallization being supplied by heat exchange from the hot cathodic solution of electrodialysis stage (a);   c. separating by centrifugation the crystalline citric acid from the concentrated solution coming from (b);   d. re-cycling the mother liquors of crystallization residual from the separating operation (c) part to the electrodialysis stage (a) and part to the stage of crystallization (b).   
     
     
       2. A process as claimed in claim 1, characterized in that the electrodialysis (a) is carried out at a temperature between 50°C and 90°C. 
     
     
       3. A process as claimed in claim 1, characterized in that the crystallization (b) of the citric acid is carried out at a temperature between 20°C and 60°C. 
     
     
       4. A process as claimed in claim 1, characterized in that the 10% by weight of the mother liquors is recycled to the electrodialysis stage (a) and the remaining 90% to the crystallization stage (b). 
     
     
       5. A process as claimed in claim 1 wherein hot cathodic solution from stage (a) is delivered first into heat exchange relation with the solution of stage (b), then into heat exchange relation with cooling water, and finally to a recovery stage for alkaline hydroxide.